Selective number electronic pulse producer



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July 4, 1950 Original Filed May 23, 1941 A. H. DICKINSON SELECiIVENUMBER ELECTRONIC PULSE PRODUCER 9 Sheets-Sheet 1 INVENTOR Arthur )1.Dickinson BY 45,

ATTORNEY Ju y 1950 A. H. DICKINSON 2,514,036

SELECTIVE NUMBER ELECTRONIC PULSE PRODUCER Original Filed May 25. 1941 aSheets-Sheet 2 INVEYNTOR Arzbz zr H. Dickinson n gezzm I ATTORNEY y 1950A. H. DICKINSON 2,514,036

SELECTIVE NUMBER ELECTRONIC PULSE PRODUCER Original Filed May 23, 1941 9Sheets-Sheet 3 ATTORNEY y 1950 A. H. DICKINSON 2,514,036 SELECTIVENUMBER ELECTRONIC PULSE PRODUCER Original Filed May 23, 1941 V 9-Sheets-Sheet 4 INVENIIOR R firflzur hf 171021115012 ATTORNEY y 1950 A.H. DICKINSON 2,514,036

SELECTIVE NUMBER ELECTRONIC PULSE PRODUCER Original Filed May 23, 1941 9Sheets-Sheet 6 flrihur Jf. fl/Minson BY Q.

ATTORNEY July 4, 1950 A. H. DICKINSON SELECTIVE NUMBER ELECTRONIC PULSEPRODUCER 9 Sheets-Sheet 7 Original Filed May 23, 1941 m& m

- m MLF INVENTOR Arthur H Dic/rmso/z ATTORNEY y 4, 1950 A. H. DICKINSON2,514,036

SELECTIVE NUMBER ELECTRONIC PULSE PRODUCER Original Filed May 23, 1941 9Sheets-Sheet 8 INVENTOR Hrlkur Zip/021172502? ATTORNEY y 4, 1950 A. H.DICKINSON 2,514,036

SELECTIVE NUMBER ELECTRONIC PULSE PRODUCER Original Fil ed May 23, 1941v 9 Sheets-Sheet 9 INVENTQR firMur/Z Mic/21226012 BYE. 65

ATTORNEY Patented July 4, 1950 SELECTIVE NUMBER ELECTRONIC PULSEPRODUCER Arthur H. Dickinson,

Greenwich, Conn., assignor to International Business MachinesCorporation, New York, N. Y., a corporation of New York Originalapplication May 23, 1941, Serial No. 394,881. Divided and thisapplication June 28, 1947, Serial No. 757,768

Claims. (Cl. 177380) The present invention relates to a selectivenumber, pulse producer for producing pulses representative of selecteddigits and embodying solely electronic means.

Mor particularly, the present invention is a division of applicantscopending application Serial No. 394,881 filed May 23, 1941 entitledAccounting Apparatus and is directed to the means of said parentapplication for producing, by solely electronic means, a number ofdiscrete electrical oscillations or pulses representative, by theirnumber, of the value of a digit selected for entry into an accumulatorwhich may be of the type disclosed in said pending parent application orany type of accumulator or computing device controllable by anelectrical manifestation.

Prior devices have been employed for producing electricalrepresentations of digits but these have employed means havingmechanical inertia. Accordingly one of the objects of the presentinvention is to provide a substantially inertialess device includingtiming means for selectively producing electrical pulses, in numberequal to the value of the digit selected.

Another object is to provide solely electronic means, controlled bydigit selectors, these same means producing a manifestationrepresentative of a single digit selected or producing selecteddiflerent manifestations, each representative of a digit of amultidenominational number selected.

A further object is to provid solely electronic means, controlled bydigit selectors, to produce a number of pulses, representative of thenines complement of a digit selected.

Another object is to provide solely electronic means, controlled bydigit selectors, to produce a number of pulses, representative of thetens complement of a digit selected.

Still another object is to provide means producing a timed manifestationrepresentative of a digit and solely electronic means controlled by saidtimed manifestation for producing a number of pulses or oscillations.representative of the digit.

A further object is to provide novel pulse producing means forselectively producing a number of pulses, each number representative ofa selected digit and comprising a source of pulses or oscillations andelectronic trigger means, operable from an initial condition to a timedsecond condition and controlling said source during one of saidconditions to produce a number of pulses representativ of a selecteddigit.

Another object is to provide a novel selective number pulse producercomprising a source 9f 2 oscillations, a blocking or gate tubecontrolling said source and means producing a timed manifestationrepresentative of a selected digit for controlling said blocking or gatetube to produce a number of pulses representative of the selected digit.

Still anotherobject is to provide a novel selective number, pulseproducer comprising a source of oscillations, a blocking or gate tubecontrolling said source, an electronic trigger controlling said blockingor gate tube and means including a digit selector for controlling saidtrigger.

A further object is to provide a novel selective number, pulse producercomprising a source of oscillations, electronic means effective tocontrol said oscillations from said source to produce a selective numberof oscillations and means rendering said electronic means inoperativeafter said selected number of oscillations is produced.

Other objects of the invention will be pointed out in the followingdescription and claims and illustrated in the accompanying drawings,which disclose, by Way of example, the principle 01 the invention andthe best mode which has been contemplated, of applying that principle.

In the drawings:

Fig. 1 is a basic wiring diagram of a novel trigger circuit employed inthe invention.

Fig. 2 is a wiring diagram of a modification of the trigger circuit ofFig. 1.

Fig. 3 is a basic wiring diagram of the electronic commutator employedin the invention.

Fig. 4, parts a and b are diagrammatic illustrations, on an enlargedscale, of pulses employed for controlling trigger elements of theelectronic commutator shown in Fig. 3 and parts 0, d and e arediagrammatic illustrations, on an enlarged scale, of voltage conditionsresulting from the operation of the trigger elements comprising saidcommutator.

Fig. 5 is a diagrammatic illustration of the grouping and arrangement ofthe figures, which assembled together constitute a complete wiringdiagram of the invention.

Figs. 5a to 5g, inclusive, grouped together and arranged as shown inFig. 5, comprise the complete wiring diagram of the invention.

Fig. 6, parts a and b are diagrammatic illustrations of wave forms ofoscillations produced in the output of an oscillator utilized in theinvention and parts c and d illustrate such wave forms, respectively,after their conversion to peaked pulses.

Fig. 7, parts a to n, inclusive, and parts p are diagrammaticillustrations of wave forms illustrating the voltage conditionsresulting from the operation of trigger elements comprising anelectronic commutator which is employed for producing control and digitrepresenting pulses.

Fig. 8, parts a. to n, inclusive, and part 1) are diagrammaticillustrations of pulses produced after conversion of the wave formsshown in Fig. '7, parts a to n, inclusive, and Fig. 7 part p, while Fig.8, part q, is a diagrammatic illustration of pulses, similarly produced.

For purposes of simplicity the electronic selective number, pulseproducer is shown as embodied in a key controlled device. It is to bespecifically understood, however, that the digit selection may be madeby a record controlled device such as comprises one of the parts of arecord controlled tabulating machine generally of the punched cardcontrolled type.

The construction and operation of various basic circuits will first bedescribed, followed by an explanation of how these circuits are employedfor producing a selected number of pulses.

1. General The means for producing these electrical pulses may comprisea series of trigger circuits, each as described presently, and connectedin cascade to form an electronic commutator producing timed pulses at anumber of index points in a machine cycle of a tabulating machine, forex ample, of the type referred to above. These timed pulses are appliedto a control trigger called an entry control which in turn controls atube referred to as a gate or blocking tube. This gate tube has appliedto it, a continuous source of pulses but normally blocks these pulsesand will permit only a chosen number to pass, when it is actuated in amanner to be described, for a length of time proportional to a. selecteddigit, whereupon said gate tube is opened or unblocked to permit anumber of pulses to pass equal to the value of a digit selected. Thelength of time that the gate tube is open depends upon the par ticulartiming of that pulse produced by said commutator and selectivelyrendered effective by a keyboard. For example, if a digit --3- is to beentered additively into a tabulator of the type referred to above, thenumber 3 key of the keyboard is depressed which closes contacts toselectively render effective the 3 timed pulse produced by thecommutator, which "3 timed pulse trips the control trigger to one of itsstable conditions to hold said trigger in said stable con dition for alength of time equal to the time separation of said 3 pulse and thepulse produced by the commutator. The trigger, while it is held in thiscondition, renders the gate tube effective to pass through, threepulses, so that it is seen that a number of pulses is produced equal tothe value of the digit key selected for operation. The various elementsof the selective number pulse producer will now be described.

2. Trigger circuit dition of stability, one of the triodes has a rel--atively low impedance and the other has a relatively high impedance. Inthe other condition of stability, the respective conditions of the twotriodes is reversed. Controlling impulses are applied to the other twovacuum tubes, which are pentodes, comprising the trigger unit to causethe shift from one condition of stability to the other. Every secondimpulse brings the trigger to the original condition of stability.

Referring to Fig. 1, voltage of the polarity indicated is supplied tolines 50 and 51 and to a voltage divider consisting of resistances 5Gand 51. Voltage is also supplied by means of the divider to line 6|, itspotential being positive with respect to line iii.

The trigger circuit comprises two impedance networks. O-ne networkincludes resistances 62a, 63a. and 64a, resistance 63a being shunted bycoupling condenser 65a. Vacuum tubes 68b and 6% shown in one envelope,in Fig. 1, are connected in parallel between point 66a, located betweenresistances 62a and 63a, and line 6!. The second impedance networkconsists of resistances 62b, 63b, and 64b, resistance 631) being shuntedby coupling condenser 65b. Vacuum tubes 68a and 69a, also shown in oneenvelope in Fig. l are connected in parallel between point 66b. locatedbetween resistances 62b and 63b. and line 6|. Resistances 62a and 62bare equal in value as are resistances 63a and 63b, and resistances 64aand 64b. The capacities of condensers 65a. and 6517 are also equal. Inactual practice an eflicient combination was found when the values ofresistances 62a and 640: were each approximately one-third the value ofresistance 63a. A suitable value for the capacity of the condenser 65ais of the order of a few hundred micromicrofarads.

Assuming that the grid of triode 68a is substantially at the samepotential as line 81, its grid bias will be substantially zero. Withresistance 62b properly chosen, triode 68a has an impedance relativelylow as compared to that of resistance 62b and its anode and point 66b towhich the anode is connected will have a voltage which is not muchgreater than that of line 6| with large current flow through triode6811. With resistances 63b and 64b properly chosen, the otential dropacross 631) is great enough to maintain point 811) and hence the grid oftriode 68b, negative with respect to line 6|. With triode 68b negativelybiased, it has an impedance greater than that of resistance 62a. Hencethe anode of triode 68b and point 660 to which the anode is connectedare at a high enough potential so that the voltage drop acrossresistance 63a will not force the potential of point 61a below that ofline iii.

The foregoin describes one condition of stability in which triode 68ahas a large current flow therethrough and triode 68b is at shut-off.hence with no current flow therethrough, and point 66a is at a higherpotential with respect to lines 6| and Si, than is point 66b. The mannerof switching the trigger circuit to the other condition of stability, isas follows.

In order to shift the trigger from one stable condition to the other,pentodes 69a and 692: may be employed. The screen grid (hereinafterdesignated as a screen) of pentode 69a is connected to a point on avoltage divider consisting of resistors 10a and Na. The potential ofthis point being positive with respect to line 6!, the screen voltage ofpentode 69a is positive with respect to its cathode. The screen ofpentode 89b is connected to a point on a. voltage divider consisting ofresistors 10b and Mb. The voltage of this point is likewise positivewith respect to line 6!, so that the screen potential of pentode 89b ispositive with respect to its cathode. The control grid (hereinafterdesignated as the grid) of pentode 69a is connected to the control gridof G9!) and both are connected to a resistance 12, to which positivepulses are applied in a manner described later. In the absence of anypulse on resistor 12, the negative grid bias of pentodes 69a and 69b isthe potential difference between lines 6| and and is sufliciently greatto maintain pentodes 69a and 69b at shut-off.

When, however, a positive pulse is applied to resistance 12, there is asimultaneous negative bias reduction of the grids of both pentodes 69aand 6%, but since the anode of pentode 69a is directly connected to thatof triode 68a and since the plate voltage of triode 68a and point 66b isvery low, this particular bias reduction is ineffective to increasecurrent flow through pentode 69a and thus has no effect on the triggercircuit. The anode of pentode 69b, however, is directly connected tothat of triode 68b and to point 66a, and since the potential of thispoint, with respect to line BI, is relatively high, the simultaneousbias reduction of pentode 89b causes a current flow as follows: Fromline 50,

resistor 62a, pentode 691), line 6|, resistance 51 to line 5!, thuscausing point 660. to suddenly drop in potential, producing a negativepulse. This negative pulse is fed through condenser 65a to the grid oftriode 68a, effecting a sudden increase in the negative grid biasthereof, and reducing current flow through triode 58a and resistance62b. Point 66b, accordingly, rises in potential, with respect to line6|, to produce a positive pulse which is fed through condenser 65b tothe grid of triode 68b, changing its grid bias to substantially zero.Since now the potential of point 6% has risen and that of point 66a hasdropped, triodes 68a and 68b assume another condition of stability whichis the reverse of that originally described, namely, triode 68a is nowshut-off while triode 6% passes a large amount of current. This newstatus of the trigger circuit will be maintained until another positivepulse is applied to resistance 12. When this occurs, the resultingnegative grid bias reduction of pentode 69b is ineffective while that ofpentode 69a is effective to increase current flow therethrough. and thetrigger is returned to the condition of stability originally described.

It may be noted that to best achieve the operations as described above,the pulses applied to the grids of pentodes 69a and 69b should be ofsteep wave form. Preferably the R. 0. product of the value of resistance12 and the value of the capacity of any associated condenser should notexceed one-fifth the R. C. product of resistance 63a and condenser 65a.It should also be noted,.that negative pulses, applied to the grids ofpentodes 69a and 69b, are ineffective, to cause the shifting actionexplained above, in the particular trigger just described Novel meansare now provided for rendering the trigger action selective which areshown and claimed in applicants divisional application Serial No. 45,924filed August 24, 1948. In the foregoing description, it is assumed thatswitches 13a and 13b are in open position, as shown. The closure ofswitch 130, shunts out a portion of resistance Ha, thus reducing thescreen potential of pentode 69a to substantially that of line 6|.Assuming that the trigger condition of stability is such that point 66bis at a high potential, this screen potential reduction prevents anynegative grid bias reduction of pentode 69a from being effective inbringing about increased current flow therethrough. Therefore, untilswitch 13a is opened, successive applications of positive pulses toresistance 12 are ineffective to change the status of the trigger fromthat condition in which points 66b and 660. are at high and lowpotentials, respectively.

Similarly, the closure of switch 13b shunts out a portion of resistance'Hb, thus reducing the screen voltage of pentode 69b to substantiallythat of line 6|. Such screen voltage reduction, when point 66a is athigh potential, prevents any negative grid bias reduction of pentode 69bfrom being effective in bringing about increased current fiowtherethrough. Therefore, under these conditions, until switch 131) isopened, successive applications of positive pulses to resistance 12 areineffective to change the status of the trigger from that condition inwhich points 66a and 66b are at high and low potentials, respectively.Switches 13a and 13b, therefore, comprise parts of selection meanswhereby selectivity in operation is obtained.

The condition of the trigger may be determined by observation of a glowdischarge (neon) tube 18, which is connected in series with a currentlimiting resistor,. between line 50 and point 65a. When point 66a is ata high potential with respect to line Bl, the difference in voltagebetween it and line 50 is insufflcient to ignite tube 18. When point66a, however, is at a low potential (point 66b at high potential), thedifference in voltage is great enough to cause neon tube 18 to fire.This indicates that the trigger, as a whole, is on.

That portion of the circuit of Fig. 1 within the broken line enclosurefinds extensive use in various portions of the electronic pulseproducer. For purposes of simplicity, this enclosed portion will behereinafter termed a trigger element and it will also be understood asdescribed in connection with the ignition of neon tuie 18 that whenpoints 661) and 66a are respectively at high and low potentials, withrespect to lines SI and 5|, the trigger element is in an on status andthat when the potentials of points 66b and 66a are respectively low andhigh, with respect to lines 6| and 5|, the trigger element is in an "offstatus. The voltages which exist at points of the trigger such as points66b and 66a, and which vary in accordance with the conditions ofstability, are employed for many control purposes, as subsequentlyexplained.

The circuit of Fig. 2 also relates to a. triggering circuit, which issubstantially similar to that just described in connection with Fig. 1.Portions of this circuit, which correspond in character and function toportions of the circuit of Fig. 1, are given the same referencecharacters. With regard to the arrangement of Fig. 2, it also may havetwo conditions of stability, but in lieu of deriving pulses from acommon source and applying them to two circuit points to shift thecondition of stability, two sources of pulses, such as resistances 12aand 12b are employed. It is assumed that such pulses do not occursimultaneously. The grid of pentode 69a is connected to resistance 12aand whenever a positive pulse, occurring atone time, on 12a is appliedto the grid of 69a, there is an increased current flow with the circuitin Fig. 1. as in the circuit of Fig. 1, are provided, since it 7 through69a, assuming that triodes 88a and "b have high and low impedances,respectively, and

the circuit shifts to a stable condition in which points 66b and 66a areat low and high potentials, respectively. With the circuit in this laststatus, a positive pulse occurring, at another time, on resistor 12breduces the negative grid bias of pentode 89b causing increased currentflow therethrough and the trigger is shifted to the opposite conditionof stability, wherein points 6611 and 68a are at high and lowpotentials, respectively or in other words the trigger, as a whole, ison. The manner in which the circuit shifts from one condition ofstability to the other is similar to that described in connectionSelection means,

is obvious that closure of switch 13a. (Fig. 2) prevents pulses appliedto resistor 12a from being eifective while the closure of switch 13bprevents pulses applied to resistor 12!) from being effective.Manipulation of switches 13a and 13b, therefore, permits selectiveoperation of the circuit. This modification of the triggering circuit,which includes the two sources of pulses, is employed extensively in thecircuits of the electronic pulse producer. That portion of the Fig. 2circuit within the broken line enclosure, is identical in structure tothat portion in Fig. 1 within the broken line, except that the controlgrids of pentodes 59a and 6% are not interconnected. This portion,therefore, is called a trigger element, and it, along with its twosources of pulses, forms the basis of the electronic commutatorpresently to be described.

While tubes 69a and 6917 have been shown as pentodes in the circuits ofFigs. 1 and 2, it will be understood that one or both of these vacuumtubes may be triodes, like tubes 68a and 68b. When tubes 59a and 69b aretriodes, however, no screen grids are available to afford the triggercircuit the novel feature of selectivity provided by the selection meansas set forth above.

:3. Electronic commutator The purpose of this commutator, which is of atype as shown and claimed in applicant's copending application, SerialNo. 394,884 filed May 23, 1941, is' to provide means whereby variousresults may be obtained at high rates of speed and without the undesiredeffects of inertia when the circuit functions continuously with respectto a given time base. The circuit employs vacuum tubes and associatedimpedances, the trigger element as employed in Fig. 2 and described insection 2, being utilized as a fundamental unit. The number of unitswhich are employed depends upon the number of steps through which it isdesired to progress before the commutator circuit repeats its function.

Assuming that one of the trigger elements comprising the commutator ison" and the remaining ones are off, the former element so conditions thenext succeeding or second element, that upon the occurrence of a pulse,termed an advancing pulse, this conditioned element is turned on. Thisnext element, in turn, when on, conditions the element just preceding,so that upon the occurrence of a pulse, termed a restoring pulse, whichoccurs prior to the next advancing pulse, the first preceding element isturned ofi. The second element, which is now on," in turn conditions athird element so that when the following advancing pulse occurs, thisthird element is switched on. In such status the third element,

so conditions the second element, that upon the occurrence of the nextrestoring pulse, the second element is turned off.

This is a general explanation or the operation of the commutator whentwo advancing and two restoring pulses cause the "on circuit position toadvance by two. Where advancing pulses no longer applied the thirdelement would stay on" and the remaining ones 011" when, however, theadvancing pulses were again applied, stepping operations would againoccur and a fourth, fifth, sixth, etc., element would be turned on insequence. Should the total number of trigger elements be ten, the firstelement would be switched on under control or the tenth one and thecommutator could thereafter repeat its cycle of operation. It is seen,therefore, that the elements are so interrelated and so intercontrol oneanother. that upon the application of succeeding advancing and restoringpulses, there is a step-by-step operation of each of the elements tofirst an on" and then to an oil status. Each element is so operated in adefinite order. and, when the final one of a series is operated, onecycle of the commutator is completed and a new cycle can be initiated.

The principle and details of operations of the electronic commutator maybe understood by re!- erence to Fig. 3 whichv illustrates a basiccircuit comprising only three positions, it being understood that thenumber of positions can be chosen as desired. The number of triggerelements in Fig. 3 is therefore three and they are designatedrespectively, as SI, S2, and S3. Portions of the circuit of 3 whichcorrespond in character and function to those of the circuit of Fig. 2are given the same reference characters.

Referring to Fig. 3 and assuming that trigger SI is on and S2 and S3 are"oif. the manner in which the latter two trigger elements are turned onin succession will now be described. It is also assumed that advancingpulses of the character shown in Fig. 40, for example, are applied toresistance 12b (Fig. 3) and that restoring pulses of the character shownin Fig. 4b, for example, are applied to resistance 12a. It is to benoted that the pulses shown in Figs. 4b and 4a are of the same frequencybut degrees out of phase. Such symmetrical separation of the pulses,however, is not essential.

The screen of pentode 69b (S2) is connected to the midpoint ll ofresistor 63b (SI) through a screen current limiting resistor 14. Byvirtue of this circuit arrangement, the screen voltage of pentode 6917(S2) is determined by that of point I1 and, if SI is oif, point 11 isnear the potential of line BI, whereas, if SI is on, point TI is at ahigh potential with respect to line GI. When the screen voltage ofpentode 69b (82) is low, a reduction of its negative grid bias has noeffect on it. That is, a low screen voltage of pentode 69b (S2) servesas a shut-oil. On the other hand, when the screen voltage of pentode 69b(S2) is high, a reduction of its negative grid bias causes increasedcurrent flow therethrough. For the normal grid bias applied to the gridof pentode 69b (S2), a rise in its screen voltage has no efiect oncurrent flow through the tube.

Assuming SI is on," point 6% (SI) and the screen of tube 69b (S2) are ata high potential, so that SI conditions S2 in order that it may beturned on, when an advancing pulse is applied to the grid of its tube69b. An advancing pulse Fig. 4a applied to resistor 12b is eiiective vialine II to reduce the negative grid bias of tube 68b (52) increasingcurrent flow therethrough and thereby tripping S2 to an on status(section 2). The rise in potential of point 66b (S2), coinciding with anadvancing pulse, is indicated in Fig. 4d. Comparisonv of this figurewith Fig. 40 indicates that momentarily, both SI and S2 are on.

The screen 01' pentode 63a (SI) is connected to the midpoint TI ofresistor 63b (S2) through a screen current limiting resistor ll. Byvirtue 01 this circuit arrangement the screen voltage of pentode 63a(SI) is determined by that of point 11 (S2). 11' S2 is off, point I1 isnear the potential of line BI, and, if S2 is on," point 11 is at a highpotential with respect to line 6|. Thus the screen voltage of pentode69a (SI) varies in the same manner. When the screen voltage of pentode69a (SI) is low, a reduction of its grid bias has no effect, that is, alow screen voltage of tube 69a (SI) acts as a shut-oil for the tube. ntheother hand, when the screen voltage of tube 69a (SI) is high, areduction of its negative grid bias causes increased current flowtherethrough. For the normal bias applied to the grid of tube 69a (SI) arise in its screen voltage has no effect on current flow through thetube.

Since, as described above, S2 is now on, point ll of S2 and the screenof tube 69a (SI) are at a high potential, so that S2 conditions SI inorder that it may be turned on when a restoring pulse is applied to thegrid of tube 69a (SI). A restoring pulse (Fig. 41)) applied to resistor12a is efiective via line 16, to reduce the grid bias of pentode 69a(SI) increasing current flow therethrough, and thereby tripping SI to ano status, in the manner described in section 2. As a result of thisoperation, point 66b (SI) drops to a low potential, as indicated in Fig.40.

If no further pulses are applied to resistances 12b and 12a, S2 remainson and SI and S3 remain ofi. This would be indicated by the fact thatthe neon tube 18 (S2 would be ignited while those related to SI and S3would be dark.

If it be assumed, however, that advancing and restoring pulses arecontinuously applied to resistances 12b and 12a, respectively, thecommutator of Fig. 3 will be continuously operated. To continue theabove description, with trigger S2 on, there is a conditioning oftrigger S3 so that the next advancing pulse applied to resistance 12b iseffective to trip on $3. The resultant potential rise of point 66b (S3)coinciding with an advancing pulse is indicated in Fig. 4e. It is seen,from a comparison of Fig. 4e with Fig. 4d, that momentarily, both S2 andS3 are on. With S3 "on," it coditions S2 so that it may be shut oil? bythe next restoring pulse on resistor 12a. The resultant potential fallof point 66b (S2) coinciding with a restoring pulse, is indicated inFig. 4d. S3 (Fig. 3) being on, also conditions SI so that it may beturned on when the succeeding advancing pulse appears on line I5. WhenSI is turned on, point 66b (SI) rises in potential, as is shown in Fig.40. SI, being on, conditions S3 so that the latter is tripped 01! uponan application of the succeeding restoring pulse to line I6. Theresultant potential fall of point 66b (S3) coinciding with a restoringpulse, is indicated in Fig. 4e.

It is now obvious that as long as advancing and restoring pulses areapplied to the commutator circuit the trigger elements SI, S2, S3, SI,and so forth, are tripped on and on sequentially and also independentlyof inductive or capacitative coupling. It is also seen that a givenelement cannot be switched on until its predecessor element is on" andthat a given element cannot be switched on until the succeeding elementis on." With this circuit arrangement, step-bystep progression, from oneelement to the next, is positive in character. This electroniccommutator is utilized in this invention as a means for sequentiallproducing timed pulses.

Further consideration of the commutator circuit of Fig. 3 indicates thatadvancing pulses, when applied to resistor 12b, are effective via line15 to concurrently reduce the negative grid bias of all pentodes 69b,each comprising a part of elements SI, S2, and S3, respectively.Likewise, restoring pulses, applied to resistor 12a, are effective vialine I6 to concurrently reduce the negative grid bias of all pentodes69a of these elements, respectively. It will be appreciated, however,that a negative grid bias reduction of a tube 69b, due to an advancingpulse, can cause increased current flow therethrough, only when itsscreen is at high potential, and such screen .is at this potential, onlywhen a preceding element is on. This preceding element is the sole onewhich is on when an advancing pulse is applied. Therefore, the reductionof grid bias for all tubes 69b is selectively effective, only in theconditioned one, and it, alone, is tripped on. It will also beunderstood that a negative grid bias reduction of a tube 69a, due to arestoring pulse, causes increased current flow therethrough, only whenits screen grid is at high potential, and such grid is at thispotential, only when a, succeeding element is On." Therefore thisreduction of negative grid bias of all tubes 69a is selectivelyeffective, only in the conditioned one, to trip it off (all otherelements, save the succeeding one, already being on and this one havingno properly related on element to trip it ofi).

Assuming, as before, that SI is on, then the screen of pentode 69b (S2)is at a high potential and an advancing pulse, which reduces its gridbias, causes increased current flow therethrough, and S2 is tripped on,as is now understood. As such action occurs, point ll (S2) begins torise in potential as does also the screen voltage of tube 69b (S3)connected to said point. It would therefore appear, at first blush, thatthe advancing pulse which trips on S2, might, by virtue of the resultingscreen voltage rise of tube 69b (S3) also cause S3 to trip to an on"status. This rise in potential of point 11 (S2) however, to its fullvalue, is not instantaneous, but occurs exponentially (see Fig. 4d) sothat an interval of time elapses from the instant of pulse applicationuntil point I1 (S2) reaches its maximum high potential and the sameapplies also to the screen voltage rise of tube 63b (S3). This timeinterval exceeds the duration of an advancing pulse so that said pulseceases to exist by the time that the screen of tube 69b (S3) reaches itsmaximum potential. Under these circumstances, pentode 69b (S3)experiences concurrently an increase of negative grid bias (because theamplitude of the advancing pulse is decreasing from its positive peakvalue) and an increase of positive screen voltage, which two conditionsoppose each other and thus prevent any substantial current flow throughthe pentode. It is seen, therefore, that only one element is tripped onfor each advancing pulse.

4. Oscillator and amplifiers A source of continuously occurringwcillatlons or pulses is required for various purposes, such as foroperating the electronic commutator, and as a source of pulses to a gatetube. Preferably, the source comprises an oscillator whose output isamplified for these purposes. Since the operation of the variouscircuits herein depends only upon the occurrence of pulses, theoscillator is not frequency stabilized and is free to drift about a meanbase frequency. Such frequency drift, great or small, does not makecircuit action any the less positive than if the frequency of theoscillator were maintained as constant as possible, since an operationor operations in any of the circuits cannot occur, unless a pulseactually exists, and no such pulse exists until the oscillator hasgenerated it. Therefore, variations in the time duration of the periodsbetween successive cycles of the oscillator are without effect on thepositive and accurate operation of the device comprising this invention.

As will be seen from the parent application Serial No. 394,881 anelectronic accumulator controlled by the pulse producing means ofinstant application functions upon a cyclical basis, there being onemachine cycle employed during the entry of a single desired amount. Theduration of time corresponding to one machine cycle determines the basefrequency of the oscillator. In said parent application, a singlemachine cycle is divided into twelve equal portions, called index pointpositions. Since a pulse may be required at any one of the twelve indexpoint positions, the oscillator must necessarily make available suchpulses which are separated by periods equal to one twelfth of a cycleduration. That is to say, the oscillator must function at a rate whichis twelve times the machine cycle rate. For example, if one cycl of anelectronic accumulator is to occur in one two hundred and fortieth of asecond or at the rate of 240 machine cycles per second, the frequency ofthe oscillator is adjusted at l2 240 or 2880 cycles per second.

The oscillator employed herein is of the type commonly known as amultivibrator. Essentially, it consists of a two-stage, resistancecoupled amplifier in which the output of the second stage is fed back tothe input of the first stage. Such an oscillator is capable of producingeither square topped or saw toothed waves, depending upon the particularpart of the oscillator circuit from which the waves are derived. Thesquare topped .waves are employed herein because they are easily changedinto pulses of extremely sharp wave front and short duration. Thecircuit diathrough the grid leak resistance 86b. The anode of triode 83bis coupled back to th grid of triode Bid by means of coupling condenser85a,

which is also connected to line 5| through the grid leak resistance 86a.With this circuit connection, the normal bias of the grids of triodes83a and 83b is zero. Such an arrangement is unstable and oscillationsare initiated by a minute change of emission of either tube. Assumingthat the current through 831: momentarily increases, this produces anincreased voltage drop across resistance 84a and a decrease in potentialacross triode 83a. This decrease is fed by coupling condenser 85b to thegrid of triode 83b, making it more negative. Current through 83b isdecreased, decreasing the voltage drop across resistance 85b andproducing an increase in potential aortas 83b. This increase is equal tothe original decrease across 83a multiplied by the amplification factorand is thus much higher. Coupling condenser 85a conveys this potentialchange to the grid of triode 83a making said grid much less negative,with a resulting rapid increase in the current through triode 83a. Thevoltage drop due to this increased current is in turn fed to triode 8312with cumulative results. Actually, the current flow through triode 83ais increased to a high value, substantially instantaneously, which flowreaches a maximum when the grid of triode 831) has a negative potentialgreat enough to reduce the current flow in triode 83b to zero. When thiscondition is reached, the charge on condenser 85b commences to leak offthrough resistance 8612, the time consumed being determined by the timeconstant of the condenser 85b and resistance 861). When this leakage iscompleted, current flow in triode 83b begins and the operation describedabove reverses, that is, the grid of triode 83a will instantaneouslybecome negative, shutting off flow through 83a and the grid of triode831) will instantaneously become slightly positive and heavy gram of themultivibrator and its principle of operation will now be described indetail.

Referring to Fig. 5a, closure of the double blade switch I9 suppliesvoltage to lines and 80, and to a voltage divider consisting ofresistances 56, 51a, 51b, 51c, and 58. Potential is also supplied bymeans of this divider to 1ines'6|,8|, 82, and 5|, their potentials beingpositive with respect to each other in the order given and with respectto line 80. The oscillator comprises triodes 83a and 83b and associatedresistances and condensers. The anodes of the respective triodes areconnected to line so through load resistors 84a and 84b and the cathodesare directly connected to line 5|.

The anode of triode 83a is coupled back to the grid of triode 8322 bymeans of coupling condenser 8512 which is also connected to line 5| flowwill occur in 83b.

It will now be understood that a heavy current flows alternately and fora given period of time through each of the triodes 83a and 83b. When oneis conducting, the other is shut off, this situation theninstantaneously reverses and said one is shut off and the otherconducts. This produces alternate and sustained voltage drops acrossresistors 84a and 84?), these voltages being 180 degrees out of phasewith each other. These voltages are in the form of square-topped waves,easily converted into pulses that possess a steep wave-front and areextremely short in duration.

Fig. 6a diagrammatically illustrates one machine cycle and shows thatthe voltages (with respect to line 5|) which occur across resistor 84:;(Fig. 5a) are as stated above, square-topped in form and occur twelvetimes per cycle. Fig. 6b also illustrates one machine cycle and showsthat the voltages (with respect to line 5|) which occur across resistor84b (Fig. 5a) are square-topped in form and occur twelve times percycle.

Since, as stated above, these voltages are 180 degrees out of phase, thepotential of point 81a (Fig. 5a) rises at each of the twelve index pointpositions and drops midway between index points while the potential ofpoint 81b rises midway between each of the twelve index point positionsand falls at each index point. One cycle of 0scillator operation is thatperiod between successive potential rises of point 81a, for example, andits time duration in seconds is equal to the sum of the time constantsof condenser 85a and resistor 86a and of condenser 85b and resistor "b,respectively.

A rise in potential of point 81a causes charging of condenser 88a andcurrent flow through resistor 89a to line 80. By suitably choosing thevalue of condenser 880 so that its recovery time is extremely short, therise in potential of 81a produces on resistor 89a, a positive pulse ofextremely short duration having a steep wave-front. A decrease in thepotential of point 810. causes condenser 88a to dischar e and a negativepulse of the character just noted is thereby produced on resistor 89a.Since the rise and fall of point Ila is constantly recurring, positiveand negative pulses are continually produced on resistance "a, of theform as shown in Fig. 60. In a similar manner, positive and negativepulses are continually produced on resistance 891) (Fig. 5a.) due to therise and fall in potential of point 81b and these pulses are illustratedin Fig. 6d. It is to be noted, that, as would be expected, the pulses onthese resistances are 180 degrees out of phase.

Pulses of the character shown in Figs. 6c and 6d are employed in manyparts of the circuit. To simplify the description, pulses, havingpositive and negative peaks occurring in time sequence, as shown in Fig.6c, are termed a-phased and lines conducting such pulses are denoted bya. Pulses, having positive and negative peaks, occurring as shown inFig. 6d, are termed bphased and lines conducting such pulses are denotedby b. These pulses, respectively, are amplified and reversed in phase,prior to utilization in various ways, such as, for example, in operatingthe electronic commutator, in controlling the selective number, pulseproduction, and in other control purposes. The amplifier circuits willnow be described.

A line 90 extends from resistor 89a to the grids of amplifying tubesBIZ) and 92b (Fig. 5a). A line 93 extends from resistor 89b to the gridof amplifying tubes illa and 92a. The anodes of tubes Ma and 9lb areconnected to line 50 through load resistors 94a and 94b, and theoathodes of these tubes are directly connected to line 5|. The anodes oftubes 92a and 92b are connected to line 50 through load resistors 95aand 95b, and the cathodes of these tubes are directly connected to line5!. Line 80 is negative with respect to line 5|, and since resistors 89aand 89b terminate in line 80, its negative potential is the normal'gridbias for tubes (Nb and 92b, and Ella and 92a.

A positive pulse on resistor 89:; reduces the negative grid bias of tube9lb, increasing current flow therethrough and the potential drop acrossresistance 94b. Condenser 96b discharges and an amplified negative pulseis produced on re-. sistance 98b. A negative pulse on resistor 89a.increases the negative grid bias of tube Blb, decreasing current flowtherethrough and the potential drop across resistance 94b. Condenser 86bbecomes more charged and an amplified positive pulse is produced onresistance 98b. It is to 14 amplified pulses on resistor 12b is similarto that described in connection with the action of tube lib. Such pulsesare similar to those shown in Fig. 6c.

The foregoing has described the manner in which an oscillator oi themultivibrator type is employed to produce square-topped waves, which areconverted into pulses of extremely sharp character, and amplified, withreversal in phase, until suitable for use in various portions of theelectronic pulse producer. It has been shown that two groups of pulsesare produced, one of positive polarity occurring at index pointpositions of a machine cycle and designated as aphased and the other ofpositive polarity occurring midway between index points and designated,as b-phased. In some few instances the negative pulses are utilized, aswill be explained in detail later. The manner in which both group 20 ofpositive pulses are employed for controlling an electronic commutatorfor producing definitely timed pulses will now be described.

5. Control of electronic commutator to continuously produce timed pulsesIn sect. 4, it was stated that the electronic accumulator operates on acyclical basis. In the accumulator of .parent application Serial No.394,881 each entry operation requires a machine cycle, which cycle isdivided into twelve equal portions, termed index point positions. Asemployed in the following description, an expression such as 1, may beconsidered to mean: the 1" time, or the 1 index point position, in acomplete machine cycle. directly by the multivibrator and which appearamplified and reversed in phase on resistors 98b, 12b (Fig. 5a) and 99b(Fig. 5e) are not tied in with a machine cycle. That is to say, no pulseappearing on these resistances can be specifically designated as a 9,"an 8, etc., pulse. Coordinating means, operated by these directlyproduced uncoordinated pulses, are provided to produce pulses which aregrouped into or tied in with a machine cycle, each pulse included in thegroup having a differential timed significance within the machine cycle.This coordinating and timed pulse producing means comprises theelectronic commutator, whose principle of operation was described above(section 3, Fig. 3). This commutator serves as a common pulse producingmeans for the keyboard and for the entry control triggers, electricalsignals representative of a digit thus being selectively produced by thekeyboard and a 55 timed pulse being applied to the entry control triggers to invariably flip them at this time. In this manner the keyboardand the entry control triggers are supplied with timed pulses which aremaintained in step with each other by the time separaac tion produced bythe commutator. The circuit diagram of this pulse producing commutatoris i1- lustrated in Figs. a, 5d and 5f. This commutator produces botha-phased and b-phased pulses and of both positive and negative polarity,at each of 05 the twelve index point positions comprising one machinecycle, and each trigger element of the commutator is capable ofproducing, one a-phased pulse and one b-phased pulse. The timed orcoordinated pulse producing means, therefore com- 70 prises twelvetrigger elements Cl2, C9 etc. Cl, C0 and Cl I, said trigger elementsbeing of the type already described (section 2, Fig. 2). Por tions ofthe commutator circuit shown in Figs. 5a, 5d and 5e which correspond incharacter and 76 function to those of the circuits shown in Figs.

Pulses, which are produced mutator comprises twelve trigger elements.

asupaa 2 and 3 are given the same reference characters. Since alltrigger elements are similar, a complete set of reference numerals isapplied onlyto CIZ (Fig. 5a).

Resistor 7222 (Fig. 5a) previously described, is similar in function toresistance 12b (Fig. 3) in that it supplies a-phased pulses continuallyto line 15 (Figs. So, 5d and 5f) whenever the machine is in operation,for the purpose of turning on the trigger elements of the electroniccommutator i. e., they are advancing pulses.

Resistance I202 (Fig. 5b) is similar in function to resistance 12a (Fig.3) in that b-phased pulses thereon are eiiective via line I6 (Figs. 5b,5a, 5d and 5e) to turn off trigger elements of the electroniccommutator. The manner in which b-phased pulses are produced onresistance 12a! (Fig. 52)) will be described later (section 9') but itis suflicient to state at this time that such pulses are continuallyapplied to line It whenever the machine is in operation.

When starting up the machine, switch IOI (Fig.- 5a) is initially closed,thereby shunting out a portion of resistance 12b and placing line 15 atthe potential of line 5|. Under this condition, pulses produced onresistance 12b are ineffective to turn on trigger elements of thecommutator.

Prior to effecting entries into the machine, the commutator isconditioned, in a manner to be described in detail in section 9, but itis sufiicient to state at this time that the result of this conditioningis to turn ofi the elements C9, C8, etc., and to turn on, solely, theelement CI2. I

Following the conditioning operation, switch II is opened, and thereuponadvancing pulses on resistance 12?) continuously control the turning onof the various trigger elements of the. electronic commutator.

The manner in which advancing and restoring pulses are employed tosequentially turn on and of! each of the elements CI2, C9, C8, etc., isas previously explained in section 3 with respect to Fig. 3. In thecircuit of Fig. 3, a commutator comprised of only three trigger elementsis illustrated, whereas in Figs. 5a, 511 and 5 the com- The principle ofsequential operation is, however, exactly similar in both commutators.From the prior description, it will be understood that each and everyone of such trigger elements becomes turned on and off sequentially,prior to a repetition of a commutator cycle, or in other words, onecomplete operation of all elements of the com mutator constitutes amachine cycle and the element CI2 demarcates the beginning andterminating point of each cycle. It is to be noted that as long as themachine is in operation and following a conditioning operation, as notedabove, advancing and restoring pulses are applied to lines 15 and I6,respectively, so that the commutator remains in continuous operation.

As previously stated, the pulses chosen as advancing pulses for thecommutator are a-phased, and in view of the explanation given in section3, it will be understood that whenever a point 66b of a trigger element,rises in potential under control of an advancing pulse (or a point 56afalls), such action occurs at an index point time. Since the restoringpulses chosen for the commutator are b-phased, it will also beappreciated that the fall in potential of a point 66b of a triggerelement, under control of a restoring pulse (or the rise of a, point561:) occurs midway between index point positions. The times in amachine cycle at which points 66b of the elements CIZ, C9, C8, etc. C0,

CH, respectively, rise to a high potential and then fall, are shown inFigs. 7a to 7L, inclusive. The times in a machine cycle at which pointsin of the elements CI2, C0, and CH rise to a high potential and [all areshown, respectively, in Figs. 7m, in, and 7p.

Figs. 7a and 71:. inclusive and '71) indicate that substantiallysquare-topped waves are sequentially produced at points 06b and 66a.These square-topped waves are converted into pulses of sharp wave-frontand of extremely short duration for selective number pulse productionand for various control purposes. Each pulse is tied in" and thus has adefinite differentially timed relationship within a machine cycle suchas 12, 9, 8," etc., which is maintained throughout machine operations,cycle by cycle.

A rise in potential of point 66b (CI2) (Fig. 5a) is'efiective, via oneof the lines in the group generally designated I02 (see also Figs. 5d,5! and 5a), to charge a condenser I03 (Fig. 5g) and to cause currentflow through resistor I04a, connected at one end to said condenser I03and at the other to line SI. The value of condenser I03 is so chosenthat its recovery time is relatively short, and therefore this .currentflow through resistor I04a is in the form of a positive short pulseoccurring at 12," which is the same as D in a cycle. Upon a fall inpotential of point 66b (CI2) (Fig. 5a) said condenser I03 (Fig. 5discharges and a pulse of negative polarity having a steep wave-frontand of extremely short duration is now produced on resistor Ma. Thepositive and negative pulses produced on resistor l04a are illustratedin Fig. 8a, and it will be observed, that as stated above, the positivepulse occurs at the 12 or D" index position and that the negative pulseoccurs midway between 91) 8.1!

In a similar manner, the rise and fall in potential of the points 66b oftrigger elements C! (Fig. 5a), C8, C1, C8, C5, and C4 (Fig. 5d), C3, C2,CI, C0, and CH (Fig. 5f) produce positive and negative pulses onresistances I04b (Fig. 5g), I040, I04d, l04e, I041, I049, I04h, I041,I04g', I04k, and ML, respectively. The difierent times in a machinecycle at which the respective pulses occur are illustrated in Figs. 8bto 8L, inclusive.

The fall and rise in potential of the point 66a of CIZ (Fig. 5a), C0(Fig. 5 and CH, produce negative and positive pulses on resistors I04m(Fig. 59), Win, and I04p, respectively. The different times in a machinecycle at which these respective pulses occur are illustrated in Figs.8m, 8n, and 81), respectively.

Consideration of Fig. 8 indicates that the positive pulses shown inFigs. 8a to 8L, inclusive, occur at the index point times and that thepositive pulses shown in Figs. 8m, 8n, and 8p occur at a point midwaybetween index point positions. Except as otherwise specifically noted,only the positive pulses are employed in this invention. It should benoted that the return circuit for re sistors I04b to I047, inclusive(Fig. 59) comprises line 82, the return circuit for resistances I04a,I04Ic, I04L, and I04p comprises line 5|, and the return circuit forresistances I04m, and I04n comprises line ill.

The foregoing has described a continuously operating commutator whichcomprises a pulse coordinating means operated by a multivibratorsupplying uncoordinated impulses to in turn produce pulses which aregrouped into repeated machine cycles, each pulse of a group having adifferential timed significance in any one cycle. The

- 17 tim'ed pulse producing means in the embodiment shown and describedcomprises an electronic commutator of twelve trigger elements.

Each of the respective "9" through "1" pulses appearing on resistanceslMb to IBM, inclusive (Fig. 59) is a "Digit Representing pulse and eachis applied to one line of a group generally designated I05 for a purposeto be explained subsequently in section 8.

The 12 or D pulse on resistor I; is effective, via line I06 (see alsoFigs. 5e and 5b), for initiating and also for terminating operation of asingle entry control device as described in sect. 8.

The pulse on resistor lMk (Fig. a) is efiective, via line llil (see alsoFigs. 5e and 5b) for terminating operation oi the manually controlledportion of the single entry control device, as will be explained insection 8.

The 11" pulse on resistor IML (Fig. 5a) is efiective via line I08 (seealso Fig. 5e) for elusive one entry as described in sect. '7.

The after D positive pulse (see Fig. 8p) obtained from 66a of CH (Fig.5!) when CM is turned oil, appears on resistor 104p (Fig. 5g) and iseffective via line I09 (see also Fig. 5e) when the device is to beutilized for subtraction, as is described subsequently in section 8.

The grids of triodes H00. and 0b (Fig. 5c) are respectively connected toresistances lillm and lllln. A pulse, negative in this case (see Fig.8m) obtained from 66a of trigger Cl! (Fig. 5a) when Cl2 is turned on,appears at 12 on 104111. and increases the negative grid bias of triodeI Ilia, decreasing current flow therethrough and the voltage drop acrossload resistance Ill. Condenser H2 becomes charged and a positive pulseis produced at 12 on resistor H3.

A negative pulse (see Fig. 8n) obtained from 66:; of trigger C0 (Fig.5}) when C0 is turned on, appears on resistor lllln at "0 and increasesthe negative grid bias of triode Hilb decreasing current flowtherethrough, and the voltage drop across load resistance Ill. CondenserH2 is charged as before and another positive pulse is produced onresistor H3, this time at 0.

Such "12 and "0 pulses appearing on resistor H3 are illustrated in Fig.8q and they are eifective, via line Ill (Figs. 5g, 5e, 5b and 50) forterminating selective pulse number production.

Having set forth the details of the electronic commutator for producingdifferentially timed impulses, a description will now be given of oneorder of the electronic accumulator, the manner of entry control foreflecting entries therein, and the manner of determining and eilectingcarry operations.

6. Selective digit representing pulse production When adding,'thetrigger control device, now to be described and of which one per orderis supplied in the accumulator of said parent application, is controlledby a timed pulse representative of a selected digit. The trigger controldevice thereupon controls a gate tube to pass pulses, whose number isequal to the digit selected, thereby electrically representing saiddigit by a number of discrete electrical manifestations, which number isequal to the value of said selected digit.

Reference to Figs. 8b to 87', inclusive, which show the digitrepresenting pulses 0 to 1, respectively, indicates that such pulseshave one positive peak only, during one machine cycle, and that suchpeaks occur at differential times in a cycle, numbered according to thedigit represented. Fig. 8b, for example, shows a "9 pulse which occurs.nine index point positions ahead or "0, Fig. 8c shows an "8 pulse whichoccurs, eight index point positions ahead of "0" etc., to Fig. 81 whichshows a "1 pulse which occurs, one index point only, ahead 01 "0." Inother words, the time interval in a machine cycle between any digitrepresenting pulse and "0" is proportional to the value 01' theparticular digit chosen to be entered and the total index points in suchinterval is numerically equal to the digit.

The trigger control device is called into action at a diil'erential timein a cycle by a digit representing pulse, referred to above, and remainsin operation until "0," so that the time interval during which thetrigger control device is operating is proportional to the value of theselected digit, and the total index points in such interval isnumerically equal to the digit. Thus a gate tube, to be describedpresently, is held open for a time interval, proportional to the valueof a selected digit and permits a number of pulses to pass, equal to theselected digit.

Referring now to Fig. 5c, the trigger control device for the tens orderof the accumulator of said parent application (which order is chosen tobest illustrate digit pulse production), comprises a trigger element aspreviously described (Figs. 1 and 2, section 2). This trigger isgenerally designated Et and portions of Ft which correspond in characterand function to those of the triggers explained in connection with Figs.1 and 2 are given the same reference characters. Triode 6b is inparallel with pentode 89b, and it can also be controlled so as to havethe same function as pentode 69b, as previously described (section 2)that is, to turn on trigger Et whenever the bias of its grid is reduced.Triodes H511 and Uta are in parallel with triode 68a, and it is to bespecifically noted that each may have the same function as pentode 69a(Fig. 2) previously described (section 2), that is, to turn off triggerEt (Fig. 50) when the bias of each respective grid is reduced.

Normally the trigger Et is of? and when se-' lective digit pulseproduction ensues, the device is turned on at a differential time. Aswill be explained subsequently (section 8), only one machine cycle isrequired and the screen of pentode 6% (Et) is at high potential duringthe complete cycle. Accordingly, a reduction in the negative controlgrid bias of pentode 69b causes trigger Et to be turned on, in a mannernow understood.

Assuming it is desired to select 3-- as the digit whose value is to berepresented by three discrete electrical pulses. The manner in whichtrigger Et is turned on at time "3 is as follows:

Referring to Fig. 5g, a "3 digit representing pulse is produced by thecommutator on resistor llllh (section 5) and is eflfective via one ofthe lines I05, digit key controlled contacts "3, closed upon depressionof the No. 3 digit key, in a manner described in said parentapplication,

- and line 8t (see also Figs. 5e, 51) and 5c) to reduce the grid bias ofpentode 69b (Et) thereby turning on trigger Et at "3 time.

With trigger Et on, its point 86b rises in potential. This rise isapplied to the screen of a gate tube 9a which is connected to themidpoint of resistor 63b (Et) through screen current limiting resistorI4. With the screen of gate tube 9a at high potential, changes in thegrid bias of this gate are now effective to vary current flowtherethrough.

Referring to Fig. 5a, it is recalled that b-phased pulses are producedon resistor 98b (section 4).

19 Line I20 extends from the grid of gate I I9a (Fig. 5c) (see also Fig.5b) to 93b.(Flg. 5a) so that the grid of gate I Isa has b-phasedimpulses continuously impressed upon it, as long as the machine is inoperation. Normally, this gate remains closed and these 12 pulses areineffective. However, when, as explained above, the screen voltage ofgate lI9a (Fig. 5c) is raised at 3" time, the positive and negativeb-phased pulses are now effective to increase and decrease,respectively, the voltage drop across load resistor I2I. Accordingly,condenser I22, discharges and charges, respectively, and a-phasednegative pulses are produced on resistance I23.

The manner in which a time pulse is produced on resistance II3 (Fig. 59)has been explained (section and this pulse is effective once eachmachine cycle via line IiI4 (see also Figs. 5e,5b and 50) to reduce thenegative grid bias of triode IISa (Et) thereby shutting off trigger Etwith an accompanying potential drop of its point 66b (Et) at "0 time.Accordingly, the screen voltage of gate II9a (Fig. 5c) falls, and theb-phased pulses continuously applied to its control grid are no longereffective to produce changes of current flow therein, and a-phasednegative pulses no longer appear on resistance I23 after 0.

Consideration of the foregoing indicates that when digit --3- isselected, trigger Et (Fig. 5c) is "on for three index point positions.During the time interval that trigger Et is on, the

screen of gate IIBa is raised in potential so that b-phased pulses whichare continuously applied to its control grid, during said interval,produce current variations therethrough. These current variations appearas a-phased negative pulses on resistance I23. The number of a-phasednegative peaks which appear on resistance I23 (Fig. 5c) is equal to thenumber of index point positions during which trigger Et is on, which inthis particular example, is three.

Resistance I23 referred to above is connected to line SI, as is also thecathode of triode II9b. Since the grid of H9?) is connected toresistance I23, its normal bia is zero and there is substantially fullflow through II9b so that a positive pulse, appearing on resistance I23has no appreciable effect on current flow through triode U IIiIb.

Since the grid of triode II9b draws current when a positive pulse isapplied to resistance I23, such pulse is attenuated by the resultantcurrent flow through I23 and therefore is almost completely lopped off.A negative pulse on I23, however, increases the negative bias on thegrid of triode IISb, reducing current flow therethrough' and the voltagedrop across resistance I24. Condenser I25 is charged and a b-phasedpositive pulse appears on resistance 12?). The number of such positivepulses which are produced on resistance 12b (Fig. 5c) is equal to thenumber of negative pulses appearing on resistance I23 because of thiscircuit arrangement. Hence, with a selection of digit 3-, only threenegative pulses occur on resistance I23, as described above, andtherefore only three positive pulses are produced on resistance 12b.Pulses on resistance 12b are applied to line I5 (Fig. 50) for thepurpose of sequentially turning on or advancing the digit manifestingelements of the accumulator of said parent application. It is to benoted, however, that these digit representing advancing pulses. areb-phased, in contradistinction to the dex pointpositions equal to theentered digit,

and that their operation is terminated at a fixed time. It has also beenshown that, as a result of such operation, discrete pulses are createdequaling the number of index point positions during which the device isoperative and thus equalling the number repres nted by the digitselected.

7. Complemental number pulse production When the accumulator of saidparent application is to subtract, operation of the trigger controldevice begins at a fixed time in the cycle instead of a selected time,as in adding. This operation continues until that index point positionis reached which position corresponds numerically to the subtrahend, atwhich differential time, suspension of this operation occurs. This isproduction of a nines complement, which is the method employed forsubtraction in said parent application. If, for example, a -6- is thedigit selected as the subtrahend, the trigger con trol element isstarted in operation at a fixed time and isstopped under control of a 6time pulse, representative of the digit 6-- selected for subtraction, asdescribed presently, a series of three pulses (the nines complement of-6) will be permitted to pass by the gate tube 90. (Fig.

Referring now to Fig. 5c, the trigger control device Eu for the unitsorder of the accumulator of said parent application is similar totrigger Et (section 6) and it is therefore not believed necessary todescribe trigger Eu in detail. The operation of the units order triggerwill be described, as it more clearly depicts operation, duringsubtraction. Normally trigger Eu is ofi, and when a after D time pulseis effective via line I4'I (as described in sec. 8), early in asubtraction cycle, the trigger is turned on. As will be ex-- plainedsubsequently, (section 8) during a single subtractive entry, only onemachine cycle elapses and further the screen of pentode 69b (Eu) is at alow potential during the complete cycle so that 69b is not operative, asit is in adding. As will also be explained later (section 8) the screensof pentodes I39a and I4fla (Fig. 5e) are at a high potential during thecomplete cycle. The manner in and time at which trigger Eu is turned onwill now be described.

Referring to Fig. 59, a after D pulse is produced on resistor I04p(section 5) and is effective via line I09 (see also Fig. 56) to reducethe negative grid bias of pentode I4Ila. Since, as stated above, thescreen potential of (la is high, this grid bias reduction increasescurrent flow through Ba and the voltage drop across load resistor I4I.Condenser I42 discharges and a negative pulse is produced on resistanceI43. The grid of triode I4Ilb is connected to resistance I43 and thenegative pulse on the latter increases the negative grid bias of triodei401), reducing current now through the tube and the voltage dropa-phased advancing pulses used in the commute- .its maximum voltage.

mucosa across load resistor I 44. Condenser I" is charged and a positivepulse is produced on resistor I. This positive after D" pulse iseffective via line I" (see also Figs. 5b and 50) to reduce the negativegrid bias of triode IISb (Eu) (Fig. 50) thereby turning on trigger Eu.With Eu on, its point 66b rises in potential at after D." This rise isapplied to the screen of gate I I9a (Fig. 5c) The manner in which a risein the screen potential of gate H90. eventually produces digitrepresenting pulses on resistor 12b is as described previously (section6). The production of these digit representing pulses is initiated at afixed time for subtractive purposes and is stopped at differential timesin accordance with the digit selected for subtraction.

The reason for turning on trigger Eu at after D, rather than at "9 asmight be expected, will be clear after considering the following: At thebeginning of a subtraction cycle, trigger Eu is oil, and it was shown inconnection with the trigger circuit (section 2, Figs. 1 and 2) that apulse, applied concurrently to both portions of said trigger, shifts itto a reverse status. Consequently, if it be supposed that 9- were thedigit selected to be subtracted and a subtraction control "9 pulse(instead of a after D pulse) were to be applied to triode IIBb (Eu)(Fig. 5c) and also a digit manifesting 9" pulse were to be concurrentlyappliedto triode II5a (Eu), (to which subtractive digit time pulses areapplied, see later), Eu would shift to an "on" status and remain sountil 0. It is required, however, when 9 is to be subtracted, thattrigger Eu. remain off. Hence, were the control for Eu, as justsupposed, digit representing pulses would be produced when none isrequired, since for nines complement of -9 is Therefore, in subtractingnine, trigger Eu must be allowed to turn on but without allowing anydigit representing pulses to be produced and must be turned off at 93'This condition is fulfilled by causing trigger Eu to turn on at V afterD so that it will be turned oil? by the "9 pulse.

Point 66b of trigger Eu begins to rise in potential at after D. Eventhough there is an accompanying rise in the screen voltage of gate II9a,no pulse appears on resistance 12b for the following reason. Theaforementioned rise of point 66b (Eu) is not instantaneous, but occursexponentially. Therefore, there is a lapse of time before point 66b (Eu)reaches its maximum high potential, and the same applies also to thescreen voltage rise of gate IIQa. This time inter- .val exceeds theduration of a pulse, which is applied to the grid of gate Ilsa (Fig.50). Hence, the pulse, applied at after D" ceases to exist by the timethat the screen oi gate, Iiila reaches Under these circumstances, gateIIBa experiences concurrently an increase of negative grid bias (becausethe amplitude of the pulse applied is decreased from its positive peakvalue) and an increase of screen voltage, which two conditions opposeeach other, so that there is no current flow through the gate.Accordingly, no negative and positive pulses are produced at after D,"on resistances I23, and 12b, respectively.

Assuming, as stated above, that it is desired to subtract a 6-. TriggerEu is turned on at after D as described above. A "6 time digitmanifesting pulse, produced on resistor IINe, (Fig. 59) (section iseffective via one of the lines of group I05, key controlled contactsII'IuO, now closed and line I Iiu (see also Figs. 5e, 51) and 5c) toreduce the negative grid bias of triode IIUa thereby turning off triggerEu at 6," with an accompanying potential drop of its point 66b (Eu).Accordingly, the screen voltage of gate Ilia (Fig. 5c) falls and digitrepresenting pulses are no longer produced on resistance 12b.Consideration of the foregoing indicates that when a digit of -6 isselected to be subtracted, Eu (Fig. 5c) is on" for three index pointpositions. During this interval, the number of pulses produced onresistance 12b is not only equal to the number of index point positions,namely three, during which Eu is on, but it is to be noted that thisnumber is equal to the nines complemental value of the subtrahend, whichin this case is 6. Thus the nines complement of a selected digit isrepresented by a series of discrete electrica. manifestations equal innumber to the nines complement of the selected digit.

In order that a true difference amount may be formed, the truecomplement of -6, namely 4, should be added in the units order. As isunderstood when employing complemental addition as a method ofsubtracting, it is necessary to add an elusive one, into the units orderof an accumulator. In the electronic accumulator of the parentapplication, provision is made for adding the elusive one and thisoperation takes place at the '11 time in a cycle. The manner in which anelusive one pulse is produced will now be described.

Referring to Fig. 59, an "11 pulse, produced on resistor IML (section5), is effective via line I08 (see also Fig. So) to reduce the negativegrid bias of pentode I39a. Since the screen voltage of pentode I39aduring subtraction is high (sec. 8) the reduction of its negative gridbias causes an increase of current flow therethrough and an increasedvoltage drop across load resistance Illa. Condenser I48 discharges and anegative pulse is produced on resistance I49. The grid of triode I391)is connected to resistance I49 and the negative pulse thereon iseffective to decrease current flow through I391) and the voltage dropacross load resistance I50. Condenser I5I is charged and a positivepulse is produced on resistance I52. This 11 pulse is effective via lineI53 (Figs. 5b, 50) to reduce the negative grid bias of triode 51),thereby turning on trigger Eu. With Eu on, its point 66b rises inpotential at 11, as does also the screen of gate II9a (Fig. 5c). Euremains in an "on status until 12 at which time it is turned off by a 12pulse applied via line H4 to the grid of triode IIGa in a mannerdescribed in said parent application. With Eu functioning in thismanner, a single pulse only, is produced on resistance 12brepresentative of the elusive one. This pulse in conjunction with thethree pulses originally produced, as described above, is equal to fourpulses or in other words the tens complement of the digit 6 selected forsubtraction.

8. Operation for multiple digit pulse production Let it be assumed thata multidenominational amount of l59- is to be additively entered into anaccumulator such as disclosed in said parent application. The operator,therefore, depresses the No. 1, No, 5 and No. 9 keys in the hundreds,tens and units orders, respectively, of the keyboard of the accumulatorof said parent application causing closure of contacts II'IhI, H5 andIIluS (Fig. 59). The closure of these contacts permits digit manifestingpulses l, "5" and "9 to initiate operations of the trigger control de-

